Belden Essential Cable Facts: Mechanical Impact

Common reasons for cable failure.

Mechanical impact and stress are two of the most common reasons for cable failure. During installation, cables are often pulled into position and crushed into small spaces. Once in place, they have to withstand twisting and flexing, and they often have to operate in harsh environments with UV light and moisture or even oils and chemicals. Sub-standard cables are simply not up to the job.

Which cable components are critical?

When it comes to mechanical impact, the key components are:

  • Insulation: a dielectric that separates the cable conductors both physically and electrically so that signal or energy transmission is maintained.
  • The cable jacket is an outer covering that protects the internal cable components from the external environment.
  • The conductor: the core of the cable that transfers energy or signals from point to point.
  • The shield: a physical barrier to help prevent the signals travelling through the conductor being subject to or becoming a source of interference.

What is the risk of mechanical impact?

Maintaining an adequate wall thickness for both cable insulation and jacket is essential for mechanical protection. During installation, a cable will often be pulled, squashed and scraped, all of which can damage the cable’s components. After installation, once a cable becomes more than just a fixed object and subject to movement, deterioration of the cable can be accelerated due to the pressure to function within a dynamic environment. The result is cable failure or the need for increased maintenance.

What is the effect of mechanical impact on sub-standard cable?

  • Pulling strain caused by rigorous installation of cables into pre-built empty conduits or ductwork, often around sharp bends, can put severe stress on the cable’s components and ultimately lead to cable failure.
  • Cables not designed to withstand twisting, flexing and movement in application will experience premature ageing and eventual failure.

What risks does this pose to a building or system?

  • System failure: breakdown of the cable's protective conductor insulation can lead to decreased signal transmission and even a complete system breakdown.
  • Fire hazard: degradation of the cable jacket and insulation will give way to the heated copper conductor and ultimately become a source of fire ignition.
  • Major maintenance and repair costs: disintegrated insulation and jacket will lead to failure of the cable and eventually the complete system, requiring costly maintenance as a result of re-installation of the cabling (often in hidden conduits and ductwork).